1. Field of the Invention
This invention relates to an improved process for the recovery of nickel from aqueous acidic solutions containing nickel values, resulting from commercial processes, and containing other metals, and employing as the last step or stage in the process an extraction step from aqueous ammoniacal solutions, with an oxime extractant, such as a ketoxime.
2. Statement of Related Art
Nickel remains one of the commercially important metals for which there is no simple solvent extraction based route for recovery from acid leach sulfate solutions. Although solvent extraction of nickel from acid sulfate solutions is possible using carboxylic acids (VERSATIC.TM. acids), and alkyl derivatives of phosphoric and phosphinic acids e.g. D2EHPA (di-2-ethylhexyl phosphoric acid), these extractants do not offer high selectivity over other metals such as manganese, iron, cobalt, magnesium and calcium. In order to achieve selective extraction of nickel, these reagents require careful pH control and multiple crowding (scrubbing) stages. In addition the VERSATIC acids are most effective for nickel extraction in the pH range of 6-8, which is above the pKa of the carboxylic functionality of approximately 5.2. This means that the VERSATIC acid will form alkali metal soaps and this leads to solubility problems with this reagent.
The liquid-liquid extraction of nickel from acid sulfate solutions was reviewed in 1973 by Warshawsky in "The Liquid-Liquid Extraction of Nickel: A Review, Minerals Sci. Engineering, Vol. 5, No. 1, January 1973, pp.36-52, and only limited progress has been made since this review. Warshawsky observed that the development of reagents which showed selectivity of nickel over other transition elements was not expected to be easy and such has been proven to be the case. The development of a suitable nickel extractant has been complicated by the fact that the nickel electrowinning is very sensitive to pH, with only a small pH window of 3.8-4.2 suitable to electrowinning, which is significantly higher than the typical pH of acid sulfate leach liquors.
Recently, interest in the recovery of nickel from laterite ores and sulfide concentrates using hydrometallurgical routes has led to a reexamination of the recovery of nickel from such ores or concentrates, which initially involve leaching with sulfuric acid to provide an acidic sulfate aqueous solution containing the nickel, along with the other metals associated therewith.
"Heterogenous Equilibria in Ammonia/ Laterite Leaching Systems" are discussed in International Laterite Symposium, by Osseo-Asre, K. and Aelhere, S. W., Ed. Evans, D. J. I., Shoemaker, R. S. and Veltman, H., SME New York, 1979, pp. 585-609.
A Cobalt Stripping process is described in U.S. Pat. No. 4,083,915 issued to Hubred, G. L. in 1975.
G. A. Kordosky et al describe "Use of pH Control in Solvent Extraction Circuits", Mining Engineering, SME New York, March 1981. pp.291-299.
"Recovery of Nickel by Liquid Ion Exchange Technology", is discussed by C. R. Merigold and R. B. Sudderth, AIME Annual Meeting, Chicago, Feb. 25-Mar. 2, 1973.
Also D. N. Nilsert et al discuss "Solvent Extraction of Nickel and Copper From Laterite-Ammoniacal leach Liquors", USBM R1 8805, 1982.
Further, I. G. Sloepper and J. E. Fittock discuss "Nickel Cobalt Separation by Ammoniacal Solvent Extraction: The Operating Experience", Proceedings of ISEC, 1996, University of Melbourne, pp.777-782.
Other items relating to extraction of Nickel are:
(1) U.S. Pat. No. 3,907,966 for Nickel Extraction and Stripping Using Oximes and Ammoniacal Carbonate Solutions issued Sep. 23, 1975 to Ronald R Skarbo.
(2) "The S.E.C. Nickel Process" by Richard D. Eliason and Edward Edmunds Jr., Hydrometallurgy, October, 1973, pp. 82-86.
(3) Commonly assigned, U.S. Pat. No. 5,470,552 for NICKEL EXTRACTION PROCESS of Kordosky et al, which discusses many other references in the related art section thereof, the disclosure of which is hereby incorporated by reference.